1. Field of the Invention
The present invention relates to a device for producing fiber preforms, which in particular are a precursor in the production of fiber reinforced plastic components. The invention moreover relates to a method for using the device to produce fiber preforms.
2. Description of the Related Art
Fiber reinforced plastic consists of a matrix material which, among other factors, provides the stiffness, and of fibers which are embedded into the matrix material and which, among other factors provide the tensile strength. Fiber reinforced plastic is used in particular for highly stressed components which nevertheless need to be as light as possible. Since the fibers do not provide strength in a transverse direction, the fibers must be oriented such that their longitudinal direction conforms as closely as possible to the respective load direction. In order to achieve this, the fibers must often be laid in different directions. The better and more precisely the positioning of the fibers is adapted to the load, the better the component will be. There are numerous production methods for fiber reinforced plastic components. Methods which are particularly appropriate for the production of large quantities are however currently only available for rotationally symmetrical or plate-shaped or respectively line-shaped components through winding or plate-pressing or respectively extrusion.
In contrast, more complex high-grade structures can only be produced at high cost, since production of the required fiber preforms is difficult, slow and expensive. High grade structures are generally produced from continuous fibers. In many processes, fiber preforms, are initially produced according to the desired three-dimensional component shape—so-called preforms—which consist predominantly of fibers which are often arranged in several layers on top of one another to achieve the necessary fiber orientation. Afterwards, the fiber preforms are impregnated or coated with the matrix material, sometimes also pressed and finally cured. For the production of the fiber preforms, as well as for impregnation and/or curing of the components, molding tools according to the desired component shape can be used onto or into which the fiber preform or the component is placed and/or pressed.
So that the fiber preforms possess sufficient dimensional stability for further processing, they are provided with small amounts of adhesives or binding agents and, following the three-dimensional draping are fixed, for example by means of drying or heating and cooling.
The fiber preforms are usually created through placing on top of one another and fixing of prefabricated and pre-joined flat semi-finished product. Such semi-finished products are for example tapes or fabrics, laid thread structure or nonwovens, wherein a multitude of individual threads or rovings are already woven, sewn or agglutinated into a flat fabric. One refers to “thread” in the use of so-called continuous fibers, in other words if the fibers are unwound from a spool or from a ball of thread. Numerous threads which are unwound untwisted simultaneously from a spool or a ball of thread are referred to as thread bundle or roving. The rovings can hereby consist of several tens of thousands of individual threads which are also referred to as filaments.
The required individual parts are cut to size according to a type of pattern from a flat semi-finished product which is usually available in the form of a roll product, as is known from DE 10 2008 011 658 A1. Then they are placed over a molding tool and joined with each other or pressed together. One example for the production of such semi-finished products by means of agglutination or sewing is also given in DE 10 2008 011 658 A1. In spite of everything however, a large amount of manual actions are often necessary. A device for machine production of simple single-dimensional curved preforms with sections of semi-finished product which are pre-stored in a cartridge and are then deposited on a core, is known from DE 10 2008 042 574 A1. More complex forms cannot yet be produced by machine.
Another possibility for producing fiber preforms for more complex components is automated fiber placement. Here, narrow thread bundles or ribbons from thread bundles guided back and forth over the molding tool by a fiber placement head, and are thereby placed adjacent and on top of one another on the molding tool, pressed onto it and fixed. For more complex components, an expensive robotic control of the fiber placement head is necessary. Even when using two, three or even four parallel fiber placement heads the production speed is still relatively slow, since the heads often have to travel long distances and since they are working successively with narrow fiber bundles. Moreover, they have a very long and complicated thread-tracking from the creel to the multi-axial moving placement head. Such thread-tracking in flexible tubes with special guide blades to prevent turning of the rovings is shown, for example in U.S. 2008/0202691 A1.
What is needed in the art is a device and a method for production of fiber preforms, so that also more complex high grade structures can be more easily automated, and manufactured faster and cheaper, however remaining flexible in shape and thread orientation.